Door closers are used to close a door after being opened manually or automatically. Generally, door closers include a cylinder having a piston connected to a piston rod within the cylinder. The piston is normally biased by a compression spring. The opposed ends of the cylinder and the piston rod may be suitably connected between a door frame and its door. The opening of the door causes the piston to be rectilinearly displaced within the inner surface of the cylinder whereby the connected piston rod is extended beyond the end of the cylinder, thereby compressing the spring. The compression spring, acting on the piston in its compressed state, normally functions to return the door to its closed position as the door is released after the opening of the door.
In certain applications, hold open rods are used to control the rate at which a door, a hatch, etc., closes. To control the closing of a door, pneumatic springs or hydraulic-type dampeners have been used to dampen the movement of hold open rods. The retracting momentum of the piston is typically cushioned by compression of fluid, such as air or oil inside the cylinder tube to create a damping resistance opposite the force that propels the door to close for better control of the speed and force at which the door closes.
A known problem regarding known dampeners is that the fluid used in these devices introduces an opportunity for undesirable leakage. In addition, these hydraulics and pneumatics have seals, wipers and o-rings that wear and require frequent maintenance and replacement.